4.2.2. Sedimentary Islands

The altitude of the sedimentary island is 0–93 m, with over 95% of areas lower than 16 m, and the flat terrain caused a high level of exploitation indirectly, including small islands with an area of 1 km<sup>2</sup> to 3 km2. Thus, the proportion of PS and LS in sedimentary islands is large.

The marine depositional plain and mudflat are the main geomorphic types of the sedimentary island, leading to the different dominant land-use types of PS and ES on the island–continent and intertidal zones. Sedimentary islands are formed by the deposition of sediment flow [55], during which more sandy lands are formed, with the low-lying wetlands evolving from tidal creeks on the island–continent. These landscapes are primarily turned into drylands and paddy fields. These islands, with a low vegetation coverage, are susceptible to desertification and storm surge invasion, so many casuarinas are cultivated for wind-breaking and sand-fixation in this area. Furthermore, the intertidal zone of the sedimentary island developed a large area of mudflat, offering the enabling environment for the mangrove forest growth and the aquaculture pond reclamation. Thus, the area and the density of aquaculture ponds far outweigh the other islands under disorderly exploitation.

#### 4.2.3. Volcanic Island

Naozhou Island features a volcanic landform, which has the altitude ranging from 0 to 81 m and decreasing outward from the crater center with a gentle slope gradient. Thus, it is intensively exploited. Since loping fields on volcanic islands with a topographic relief gradient between 10–40 m lack surface water, many drought-tolerant crops are planted in this area, such as sweet potatoes, peanuts, and mung beans. Combined with the field research, local literature, and historical satellite maps, it is found that some lagoon and ancient lagoon landforms were developed on the coast and intertidal zone. The formation of harbor lands mainly relies on the lagoon landforms. While the wetlands mostly evolved from ancient lagoons and most reservoirs, paddy fields were exploited on this geomorphic type.
